Production of sintered articles



April 29, 1941. H. VOGT EI'AL PRODUCTION OF SINTERED ARTICLES Filed Jan. 30, 19:59

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assesses la t,- a, ii

at are FRQDEICTXQN SMERli-iiil AR'EKCEES Mans Vogt, Ecrlin-Neuholln, and Ernst mots,

fier fiermsdori, Gerry; said hilota signer to said. Vest Application .liany 3t 1939, Serial No. 253,654 In Germany Feb 1 d 1938 14 Claims.

tion is to reduce the shrinking of such porous articles in the sintering operation.

Still another object is to prevent corrosion in the inner structure of porous metal articles.

A. special object of the invention is to provide a method of producing porous anti-friction metal, especially from iron, having a substan-' tial oil absorbing capacity and great mechanical strength.

A further object is to improve the running in characteristics of such porous bearings and to reduce the coefiicient of friction thereof.

A still further object is to produce metal Wicks. packing rings and the like of high porosity and mechanical strength.

With these and further objects in view which will be apparent from the within disclosure, our invention comprises broadly the addition of metal compounds, more particularly metal oxide and metal salts to the metal which forms the porous sintered body and the reduction to metal of said metal compound additions.

(on, $5 -22) a tained by the addition of metal compounds in the form ofsolid particles.

We give the following examples'of our process,

but it will be understood that while in said examples we refer to certain materials and to oer- 'tain articles produced by the process of the present invention, other materials may also be used and the particular structure may be used in other articles. It will be understood further that the analysis of the product will vary according to the raw materials used in its manufacture, and that the characteristics of the resulting product and the steps in the process may be varied considerably. I

Where it is mainly intended to enhance the -mechanical strength of the sintered body, we pref-fer to add the metal compounds in the form of'a organic acid salts and carbonates of the heavy metals, more particularly of the group comprising iron, nickelchromium, cobalt, manganese 1 or copper. The impregnation of the porous It is to be understood, of course. that the present invention is not to be limited to production of the sintered bodies from the particular sources metal particles with the metal salt solution may be carried out repeatedly and a reducing opera tion may be inserted after each impregnating operation. The metal salts may be dissolved in water, glycerine or the like and preferably in.

high-boiling solvents, for example, polyvalent alcohols. -It is also possible to impregnate the sintered body with the metal salt solution, in this Fig. 2 is a sectional view, made up after the case the body must be subjected to a further heat 1 treating, sintering or reducing operation.

Example 1 Relativelyv coarse spongy iron particles (sponge iron) are compressed or briquette'd to a bearing bushing or the like, for example, in the form shown in Fig. 1. In this compressed state, the material has a specific gravity of 5. and a per centage by volume of pores ofabout 33%. The

briquette is then impregnated with a saturated aqueous solution of sulfate of iron, under vacuum, and dried by action of ahot air current, until the waterhas been evaporated completely. The briquette which now shows the sea-green colour of the iron sulfate deposit is then sintered This value has been found by a crushing test to which a bearing bushing made according to the 'invention was subjected, together with a second bearing bushing made in the same manner, but without impregnation. The latter piece was crushed after 14 shocks while the bushing'made according to the example was crushed after 34 shocks. The shrinking which generally amounts to 0.35 percent, was found to be unchanged by the impregnation.

It is also contemplated that the sintered article may be rendered more corrosion-proof by the use of certain salts for the impregnation. For example, nickel salts or chromium salts may be used to increase the resistance of the surface of porous iron structures. Also, where the base metal shows undesirable catalytic features, for example, with respect to the decomposition of the lubricant, such catalytic effects may be prevented in this manner. For instance, self-lubricating bearing materials in which copper which tends to accelerate said decomposition represents a substantial component may thus be provided with an interior protective coating of a metal, for instance, iron, which has no catalytic or other detrimental effect.

The improved mechanical strength attained by our novel process is probably due to the fact that by a capillary effect the metal salt solution is drawn into the narrow spaces at the points of contact between adjacent particles whereby the respective metal is deposited in these narrow spaces and in the melting or sintering operation, enlarges the point-shaped contact points to larger areas thus producing a greater mechanical strength.

It is also contemplated that the metal salt *shall be dissolved in a solvent of high boiling point, for example, a polyvalent alcohol, in order' to prevent the solvent from evaporating already during the mixing phase of the metal powder.

The impregnating and reducing operations may be repeated several times, and different metal salt salts of various metals may be used provided that I they are capable of withstanding the pressures exerted in the briquetting operation.

Example 2 Sponge iron powder substantially of a particle size of about 0.05 to 0.2 mm. is mixed with 2 to 3 with additions of about 1% oil which prevents demixing and facilitates the pressing operation, the mixture is briquetted under suitable pressure and reduced and sintered in the presence of hydrogen, at a temperature of about 1050 C. The struc- .ture thus obtained is shown in Fig. 3, right hand other purposes.

- deposited at the portion adjacent to the points solutions may be used in the successive operaadditional cavities in the porous sintered body.

we add the metal compounds advantageously in the form of solid particles, substantially of a size of 0.1 to 1 mm., to the loose metal powder, and preferably we use a metal compound comprising the same metal as the base metal powder. In this case, the size and shape of the hollow spaces produced in the sintered body by the said solid additions can be controlled by the size and shape of the metal compound particles which are added to the metal particles to be briquetted and sintered together. For example, the said metal compound particles may be round or angular, with a diameter of 0.2 to 0.5 mm., and they may be added in quantities of up to 10, but preferably 2 to 4 percent by volume. Very fine, dust-like material.

is not generally suitable because it tends to reduce the strength and to increase the shrinkage. Any reducible metal compounds, for example, chlorides, sulfates, hydrates and organic acid where the iron particles :1 contact each other,

whereby an additional bond is formed between the particles and the mechanical strength of the material is improved.

Example 3 A sintered article is made in the manner stated under Example 2 and, when cooled down, is im- 'pregnated with a saturated iron sulfate solution,

dried in a heated air current and once more subjected to the reducing-and sintering operation at the same temperature of about 1050 C.,-whereby' its mechanical strength can be further increased.

It is thus possible to increase the porosityof porous metal articles by 30 to percent, without anyreduction of the mechanical strength of the article and without any increase of the shrinkage. substantially increased and the running-in charaoteristics and the coeflicient of friction are im-, proved. In view of the larger size of the cavities or pores formed'by the metal compound additions the decomposition products occurring by oxidation and polymerisation of the lubricants e. g. bitumen, asphalt and the like, can be easily deposited and prevented from exerting a detrimental effect upon the lubrication.

It will be understood that it is also possible.

- and of special advantage, to combine steps of the 7 may be used as anti-friction material, as metal wicks forv petroleum lamps or burners, filters, catalyzators, resistances, damping plates for sound mufliers in autocars and the like.

Porous self-lubricating bearings may be made i e. g. of. iron or bronze powder and in the second case, a copper salt, for example, copper sulfate is advantageously used instead of iron sulfate mentioned in the above. examples.

The oil-absorbing capacity is thus We claim:

1. Process for the production of porous-metal bodies which comprises forming a body of the finely divided metal, introducing a metal salt into the formed body in the form of a solution thereof and reducing the metal salt to metal in situ.

2. Process as defined in claim 1 in which the finely divided metal is'formed into a body, sintered and then impregnated with metal salt solution.

3. Process as defined in claim 1 in which the metal powder mixed with finely divided metal compound is briquetted and sintered with reduction of the metal compound and the sintered briquette is impregnated with a solution of metal salt, dried and sintered. H

4. Process as defined in claim 1 in which metal powder is wetted with metal salt solution, briquetted, dried, sintered and reduced and then impregnated with metal salt solution dried, sintered and reduced.

it, mixed with finely divided metal compound is briquetted and sintered with reduction of the metal compound and the sintered briquette is im- L pregnated with a solution'of metal salt, dried and sintered.

8. Process as definedin claim 1 in which the finely divided metal is sponge iron and in which it is wetted with metal salt solution, briquetted, dried, sintered and reduced and then impregnated with metal salt solution dried, sintered and reduced.

9. Process for the production of porous metal bodies which comprises mixing porous sponge iron powder with a relatively small proportion of a metal compound, compressing the mixture to a coherent body, relieving the pressure, and sintering said. body under reduction of said metal com pound in situ whereby an additional bond is formed between the particles of the sponge iron powder and the mechanical strength of the body is increased.

10. Process as defined in claim 9 in which the 'metal compound is a metal salt.

11. Process as defined in claim 9 in which the metal compound is in solid form. g 12. Process as defined in claim 9 in which the metal compound is an iron salt.

13. Process as defined in claim 9 in which the metal compound is in solid form and has a particle size from 0.1 to 1 mm. I

14. Process as defined in claim 9 in which the sponge iron powder is wetted with a solution of a metal salt.

HANS VOG'I'. ERNST KLOTZ. 

